Merge branch 'tracerestrict-sx' into jgrpp

# Conflicts:
#	src/command.cpp
#	src/group_gui.cpp
#	src/lang/english.txt
#	src/saveload/extended_ver_sl.cpp
#	src/settings_gui.cpp
#	src/tracerestrict.cpp
#	src/tracerestrict.h
#	src/tracerestrict_gui.cpp
#	src/vehicle_gui.cpp
#	src/vehicle_gui_base.h
#	src/vehiclelist.cpp
#	src/window_type.h

src/window_type.h

@@ -712,6 +712,12 @@ enum WindowClass {
 	 */
 	WC_TRACE_RESTRICT,
 
+	/**
+	 * Trace restrict slot window; %Window numbers:
+	 *   - Packed value = #SlotListWidgets / #VehicleListWidgets
+	 */
+	WC_TRACE_RESTRICT_SLOTS,
+
 	/**
 	 * Programmable signals window
 	 */